Interchangeable pieces

Hello, I have buy a set of VM28ss of a kz1000. But the needle is not an adjustable needle.. I finally found a set of rebuilt carb of kz900 vm26ss.. with an adjustable needle.. can I use these needle and jet needle for mine?! And do I make a good move to use them if it fit?!
Thank youuu 

I take it they are 28mm pumpers.
The needle is fixed in the equivalent of the middle position and there is no real reason to change it.
If you are running without the airbox and fitting pods etc they would remain in the middle with air corrector jets installed.
You could try the adjustable vm26 needles but you will likely end up with them in the middle groove anyway.

 

I understand!! But I rebuilt my 750 with porting and oversize, pods filter (don’t have the original air box). I thinking that adjustable needle will be necessary for a good tune up on dyno ?!

The 1976 carbs used a 5DL31 needle mounted in the middle position and matched to an O6 needle jet.   I don't know the jet series but am going to guess it's 243, whiich was the series used in 1975. 

The only 28 mm carbs with only one needle position were the ones used in 1980.  They have 5CN29 needles matched to an O4 Series 259 needle jet.

Both needles are double taper (hence the two letters DL and CN) but they are different tapers.  Again, I'm guessing, but the 5DL31 needles are probably larger diameter because the needle jet (O6) is larger diameter.  So I don't think it would work in the 28 mm carbs with the smaller diameter (O4) needle jet.

The only way to tell for sure is to try them.  As an alternative, if you have the 26 mm carbs you can remove the needle jets from the 26 mm carbs and install them in the 28 mm carbs, along with the 26 mm needles.

For your information, I ride a 1980 KZ1000 with s set of 26 mm 1976 version carbs.

Thank you!! I have buy the 28mm carburetor and the guy didn’t remember on what bike they was!! So thank you very much for your explication. I dont know if I might buy a DynoJet kit for the needle set up only?! Because my dyno shop want to use the real mikuni jet!! Really hard to find the needle with tap and the needle jet!! 

Those 28's will be from 1015cc Z1R, MK2, ST or LTD..
If you are going to mix and match you may be better to spec the 28 bodies with the 26 internals and increase the main slightly for the larger bore and possibly disable the accelerator pump..
This will simply make them the equivalent of a set or bored out 26's.
The jet needle, needle jet etc work in conjunction with the slide cutaway so if the 28 slides are richer or leaner than the 26's you should use the 26 slides in the 28 bodies if using the 26's components.
If they are the same then retain the 28's slides.
When i bore these 26's out to 30mm it's only the main jet that gets increased and the rest remains stock and they perform flawlessly.
You don't need a dynojet kit for these VM's, just air correctors to cure the off idle hesitation if not running the stock airbox.
You keep all the stock Mikuni internals on stock settings and only increase the main jet a size.
With you using these carbs on a 750 you should start with the stock 28's with all the stock internals ( or spec'd as 26's) and work from there then only make one change at a time otherwise you won't know which changes contributed to a positive or negative effect.



 

All right, but my carbs hadn’t an Accelerator pump!!  (I heard that they were more difficult to tune.)  I only want a adjustable Needle for the dyno!! Mine is not.. and I dont want to play with shims under needle like my old stock CV34!!

I'm in the UK.
The only 28's that had a fixed needle here were the ones with accel pump which led me to believe that's what you had.
These were/are US import sets that came from emmisions regs machines with fixed settings to prevent tampering.
Never had a normal set with a fixed needle.
The home market VM28's here all have the adjustable needle.
Without sourcing the correct vm28 adjustable needles i would just start with the 26's needle and go from there.
As previously stated , one change at a time..


 

I agree with zed1015 that the only 28 mm carbs with fixed needles were the 1980 version.  They also all had the accelerator pump, but yours may also have had the pump removed.  Photos would be helpful.

You can find good kits for carburetors here.  I will only use Keyster in my carburetors.

www.keyster.ca/

I understand, but I don’t have any accelerator pump on my carburetor!!!  So I don’t know what kind of needle my 28’s has .. thank youu

There should be an ID stamped on the carb set.  It is most often on the flange below the choke lever, though may be on the same flange on the outside of carb #4. (carbs are as you sit on the bike from left to right 1,2,3,4) I have attached a pic, a set of vm24ss carbs that show this location, 

With this ID we may be able to tell you more about what model they came stock on and what internals they had. 

Excuse my simplicity but why don’t you pull your slides and actually see what needles and NJ are in the carbs. All this talk needs some action.